On-Die Input Capacitive Divider for SerDes Loopback Testing
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Solution Overview
Problem
Conventional SerDes loopback testing methods either fail to provide full functional coverage, add load to the main data path, or suffer from DC current and common-mode compatibility issues, making them inefficient and potentially detrimental to mission mode performance.
Innovation Solution
An on-die input capacitive divider with an integrated serial loopback circuit using an AC coupled input network, which reuses existing components to inject the loopback signal through an AC coupling capacitor, eliminating DC current and common-mode compatibility issues while maintaining minimal impact on mission mode performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional loopback testing methods are used, then test coverage is achieved, but DC current issues and common-mode compatibility problems occur
Solution Approach 1:
An AC coupling capacitor is introduced as an intermediary component between the loopback signal path and the main data path. This capacitor blocks DC current while allowing AC test signals to pass, thereby eliminating DC current issues and common-mode compatibility problems while maintaining full functional test coverage
Solution Approach 2:
The input network is segmented into separate AC-coupled paths: one for mission mode data and another for loopback testing. This segmentation isolates the test signal from the main data path, preventing harmful DC current and common-mode interference from affecting normal operation while enabling comprehensive functional testing
2Reliability
If additional components are added for loopback testing, then test functionality is improved, but device complexity and overhead increase
Solution Approach 1:
The AC coupling capacitor and associated components are designed to serve dual purposes: they function as part of the normal input network during mission mode while simultaneously enabling loopback testing when activated. This multi-functionality eliminates the need for entirely separate test components, reducing overall device complexity and overhead
Solution Approach 2:
The loopback test circuitry is merged with the existing AC coupled input network structure. By combining test functionality with the existing input path infrastructure, the patent avoids adding significant complexity while achieving full functional test coverage through shared components
3Reliability
If high drive strength drivers are used for loopback signaling, then signal integrity is improved, but power consumption and impact on mission mode performance increase
Solution Approach 1:
The AC coupling capacitor acts as a mediator that enables efficient AC signal coupling without requiring high drive strength. The capacitor's reactance at test frequencies provides sufficient signal coupling while isolating the low-power loopback driver from the main data path, thereby maintaining signal integrity with minimal power consumption and no impact on mission mode performance
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution achieves broader functional coverage with reduced diagnostic time, increased testability, and robustness against electrostatic discharge, without requiring high drive strength drivers or additional components, ensuring full functional test coverage with minimal overhead on the SerDes.
Implementation Method 1
An on-die input capacitive divider with an integrated serial loopback circuit using an AC coupled input network, which reuses existing components to inject the loopback signal through an AC coupling capacitor
Data Source
Figure 1A~1C
Figure 2
Figure 3
AI summary
There is provided an integrated loopback used for on-die self-test and diagnosis of transceiver faults. According to embodiments, there is provided an interface network including an AC coupling capacitor interposed between input pins of the interface network and an input of an amplifier, a shunt capacitor interposed between the AC coupling capacitor and the input of the amplifier and a selector. The selector includes a mission mode circuit component connected to a bottom plate of the shunt capacitor and the selector is configured to select between a first mode and a second mode, wherein the first mode is mission mode and the second mode is loopback mode, wherein in the second mode the mission mode circuit component forms at least part of a circuit that supplies a loopback signal.